I have thought about that too, in both cases it indeed makes little sense to trade masters. Yoda is at least as powerful as the Emperor, and Luke is more powerful than Snoke.

Yoda seemed to have been in good standing with Dooku when their ways parted. Dooku still called him Master Yoda after he shows his true colors. If I recall well the emperor motivated Dooku with the conquest of the Galaxy, something that Yoda could and would never give him. So Dooku has not an inferiority problem and his motive was probably rulership in sith stlye.I don´t know how Ren became obsessed with Vader. Vader was literally the shell of a man and Luke surely did not sugarcoat Ren with the capabilities and limitations of his grandfather. Luke and he tied in laser duels. Snoke is without a doubt powerful but obviously not good enough to challenge Luke face to face. Luke was taught by Yoda himself, whoever trained Snoke could not have kept up with that, so the "You could not teach me anymore" motive falls flat. Luke admits that Ren is very powerful , so the "My uncle is jealous" motive also seems unreasonable.

It's worth noting that Qui-gon Jinn was Dooku's apprentice, and that he was shattered and heartbroken after his death at the hands of Darth Maul. But the main reason for Dooku leaving the Jedi Order, reclaiming his former title as a Count on his Homeworld, and then later become a Sith to form the Separatist Confederacy was because he was disillusioned by the corruption within the Republic, the Galactic Senate, and even some within the Jedi Order and wanted nothing to do with it anymore an he left the Order before the Battle of Naboo, although some sources say that he left when Qui-gon died due to his attachment to his student as well, but none of certain and could be either. But after being tempted by Palpatine as Darth Sidious to be given the chance to overthrow the Republic he jumped in on it, even though the reality was that Palpatine just saw Dooku as a tool for instigating the Clone Wars and destroy the Jedi with Order 66.

And I would have to agree with Dooku in his view on the republic, the senate and by extension the alliance too. It is a horribly slow mockery of a governmental body, light on the military side with a wide variety of cowardly wusses and easily sidelined with some bureacratic difficulties as the emperor put them through.

The Mon Calmari, despite their peaceful and intellectual nature are probably the only race with capable military leaders fighting for the alliance. Both times the Alliance fights back against the empire with a fleet the executing Admiral is a Mon Calmari as everyone else is already on the run then.

Lol, Mark Hamil suddenly found his balls and spoke about how he would have played Luke differently but the director wanted him to be a quitter wuss so he still played it with the idea that it was not his story anymore. Looks like he was still a little bit proud of playing Luke Skywalker.^^